Mechanical Systems 399
- Universal motors (AC/DC) motors used for many types of portable
tools and appliances, such as electric drills, saws, office machines,
mixers, blenders, sewing machines, and vacuum cleaners. They op-
erate at speeds up to 20,000 r/min and have easy speed control.
Remember that AC induction motors do not have speed control ca-
pability without the addition of expensive auxiliary equipment.
Thr ee-phase AC motors of the induction type are very simple in con-
struction, rugged, and reliable in operation. They are less expensive (per
horsepower) than other motors. Applications of three-phase induction
motors include industrial and commercial equipment and machine tools.
Three-phase AC synchronous motors run at constant speeds and may be
used for power factor correction of electrical power systems. However,
they are expensive, require maintenance of brushes/slip rings, and need a
separate DC power supply.